If you feel 'nostalgic' then go ahead and try it - not only is
the lighting system different (and more vivid!), but there are only
two biomes! Many of the things implemented from the full version
are not on Alpha, but that's what makes the original Minecraft so
simple, and for some (including me!), it is good that Minecraft was
simple. I'd recommend to give it a try - Beta also has its own
experience as well. The lighting system was slightly updated, and I
believe this is when the first workings to what you currently see
in the lighting system was implemented, later in Beta.
You might also want to know that previous versions of Minecraft are extremely buggy and lack certain features.